The second episode was particularly so (IMHO): Following in the footsteps (at times literally) of Sir David Attenborough (Frozen Planet) and Professor Brian Cox (Wonders of the Universe), co-presenters Kate Humble and Dr Helen Czerski went to extra-ordinary lengths and amazing locations to explain the vagaries of the Earth’s climate past, present, and future.

For example, whereas I have previously got myself in a terrible mess trying to explain the causes of Ice Ages (as indeed it is at least arguable that James Hansen did in Storms of my Grandchildren), Humble and Czerski accomplish this with ease (and the help of some excellent computerised animation). For those of you without access to the BBC’s iPlayer; and/or those that cannot wait for the programme to be broadcast in your home country (as I am sure it will be eventually), I will try and summarise the three aspects to the Earth’s orbit around the Sun that contribute towards the occurrence of Ice Ages:
1. The date on which the Earth comes closest to the Sun during its elliptical orbit (i.e. Perihelion).
2. The extent to which the Earth’s orbit deviates from near-circularity (i.e. eccentricity).
3. The angle at which the Earth’s axis of rotation is tilted from vertical (i.e. perpendicular to the plane around the Sun in which its orbit lies).

All of these things are caused by gravitational interaction between all the planets in our solar system and the Sun itself; they are all therefore highly predictable even if not all regular and, therefore, once we understand these changes, we can trace their effects back through time. We can of course also calculate their effects today.

For example, perihelion currently occurs on January the third each year, whereupon the Earth is 5 million miles closer to the Sun than it is in July; which equates to 7% more energy input from the Sun. However, any effect this might have is more than cancelled out by the 23 degree tilt of the Earth’s axis of rotation away from the Sun causing a 50% reduction of insolar radiation to the northern hemisphere in winter.

Meanwhile, despite receiving 7% more insolar radiation from the Sun, summers in the southern hemisphere are on average 4 Celsius cooler than those on the northern hemisphere!!! Indeed, if you go 55 degrees south of the equator (e.g. southern Chile) you will find glaciers not seen in the English Lake District for several millennia. The reason for this discrepancy turns out to be the presence of the Great Southern Ocean… Whereas the seas surrounding the UK have a moderating influence on climate (avoiding the temperature extremes of Eastern Europe and Russia), the general absence of land in the southern hemisphere (which warms up faster than the oceans) has on overall cooling effect on climate.

It turns out that heat capacity is fundamentally important. Although the oceans are slower to respond to energy input (i.e. they have a higher heat capacity), the land also takes time to gain and to lose heat. This is the reason why the coldest day of the year in the northern hemisphere is often on or around the 19th of January; but why ice road truckers can continue to drive across frozen lakes in northwest of Canada well into March.

So, to get back to Ice Ages, I really don’t understand how we ever thought we were heading for one, or why some people still say we might be heading for one. This is because, in order for an Ice Age to occur, all three of the above-mentioned cycles must coincide to cause cooler summers in the northern hemisphere where most of the land is and therefore where most ice can develop and not melt (in order for glacier formation to begin). At the moment, perihelion is the only factor promoting this; and it will not coincide with extreme eccentricity and minimum angle of tilt for another 60 thousand years.

Meanwhile, we just have a slight problem of anthropogenic climate disruption to deal with.

If you remain unconvinced, please watch this brilliant 7-minute video produced by the Pacific Institute for Climate Solutions (and remember even if we stopped burning fossil fuels tomorrow, CO2 rise [and therefore warming] would continue for decades)…

15 Responses

I am an admirer of Kate Humble who demonstrates that sense of adventure that one would expect from the granddaughter of the exuberant pilot and test pilot Bill Humble who test flew Hurricane, Typhoon, Tempest, Fury and Sea Fury types as well as jet prototypes after WW2. Sadly I never met Bill, but having talked with the late Neville Duke and Peter Twiss my guess is that he was, in a social setting, a real gentleman.

Kate’s sojourn with the Afar peoples for the production of The Hottest Place on Earth was memorable for her courage interacting with those potentially dangerous peoples, the males of which could easily ‘resent’ their women being approached by outsiders.

As for explaining the progression of ice ages and describing such, yes it is tricky ground with Dansgaard-Oeschger events, Heinrich events, Younger Dryas, the 8.2k (year) event, complex issues to do with evaluating information stored in ice core and ocean and lake bed cores from both hemispheres and much more.

Watch out too for books by Richard Corefield such as ‘Architects of Eternity’ which contains much more useful background. I had the luck to be able to attend a seminar given by him about two years ago which was informative and managed to purchase some copies of his books, two for my father.

Richard Fortey writes very readable books on geology, which can also fill in some gaps.

For those who like to appreciate the whole of Earth’s geological time and its divisions you may find the Time Spiral diagram here of use. I produced this some ten years ago and have updated with extra info since but have yet to upload the new version, which I will do if there is much interest.

Thanks Lionel. I watched the third and final episode of Orbit last night and it had a very good section about human habitation of the Sahara up until about 5,000 years ago; and suggested that (all other things being equal) monsoon rains could return to the desert in about 15,000 years time…

The only problem here being that all things are not equal and, as James Hansen has pointed out, artificial interference in the Earth’s climate is about ten times the magnitude of the naturally-induced changes the Earth has been through in the last 1 million years. That being the case, if humanity manages to avoid the runaway greenhouse effect, we will retain the ability to cancel out any natural cooling by releasing more CO2 into the atmosphere.

This may sound like a victory for the Enlightenment thinking that we are superior to nature and can control it but, first of all, we still have to prevent the runaway greenhouse effect from taking hold. Unfortunately this now appears to be no trivial task.

I noticed an irregularity towards the bottom of that revised Time Spiral diagram which happened when exporting from a vector diagram (Xara) out to JPEG. This was due to a change between Xara versions in respect of handling revisions and copies. There was a copy of the diagram lurking on another pane which became grouped during the export process. This has now been fixed in the jpg version now on the web site.

The earth is cooling, it is a well known fact that has been known since the days of Lord Kelvin, however this cooling effect is one that will take eons to occur; climate skeptics knowing this little known fact use Lord Kelvin’s ideas in order to try to convince the gullible that the Earth is cooling right now under our feet and that Global Warming is a myth. The fools even use his formulas.

It’s nothing more than the use of science to deceive those who don’t understand the workings of planetary thermodynamics ……. One can’t blame those who are deceived through their lack of knowledge but the deceivers (skeptics) should be ashamed of the damage they are causing to future generations, all this does is help to delay any possible solutions and brings us closer and closer to destruction. :-(

For clarity, all readers should note that what is being referred to here is the fact that the Earth has been cooling ever since it was formed; just as the Earth’s rate of spin has reduced over cosmological time (from over 400 days per year to the current ~365); and the fact that the Moon is slowly moving away from the Earth. None of which should be of the slightest concern to any of us as there is nothing we can do about any of these things. However, the one thing we should be concerned about is the one thing we may still have a chance to stop happening – and that is to prevent human activity from turning the Earth into Venus Mk 2.0

Yes, the Republicans and the right wing think tanks have done a magnificent job of ruining virtually any chance we have of fixing the world for our future generations. We need some action and we need it now, so I believe Obama should muster his “cojones” and start making a move towards finding proper solutions.

Even though he’s muzzled why is he not screaming for people to do something? The apathy of politicians and their lack of moral fiber towards facing up to global warming is something that should not be tolerated.